Nationwide this means there will be 30 million more men than women by 2020, making it difficult for those particularly with low income or little education to find a wife, the report said.

"The increasing difficulties men face finding wives may lead to social instability," the report said.

The report went on: "We need to develop a 'movement to embrace girls'... and effectively contain the trend towards greater gender imbalances."

The report also said that China's current 1.3 billion population would grow by 200 million by 2033.

And the number of 60-year-olds and over will jump from the current 143 million to 430 million by 2040, 30% of the total population.

The country will need to improve its social security and retirement system, as well as its family planning policies and education and health services, the report concludes.

The BBC's Daniel Griffiths, in Beijing, says the one-child policy has already led to other major problems, with many single children facing the prospect of supporting two parents and four grandparents well into their old age.